Method, electric circuit arrangement and electric memory unit for determining a characteristic status parameter of the memory unit

ABSTRACT

The invention relates to a method for determining a characteristic status parameter of a memory unit via an electric circuit arrangement. In the circuit arrangement at least one inductive component and at least one capacitive component are arranged, forming a tuned circuit with the memory unit. The method has the following steps of energizing the tend circuit by temporary charging of the capacitive component, the energizing being carried out by an energizing device electrically supplied by the memory unit, and determining a time-dependent voltage change at the capacitive component after terminating the energizing and determining the characteristic status parameter from the time-dependence of the voltage change. The invention further relates to a corresponding electrical circuit arrangement and an electrical memory, including such a circuit arrangement.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 35 USC 371 application of PCT/EP 2010/050384 filedon Jan. 14, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for determining a characteristicstatus parameter of a memory unit by means of an electric circuitarrangement.

2. Description of the Prior Art

In such a method, as the characteristic status parameter, the agingstatus of the memory unit is determined by means of an electric circuitarrangement. The electric memory unit is a single electric memory cellor a plurality of memory cells electrically interconnected to oneanother, in particular an electric memory. This kind of electric memoryis for example a rechargeable battery.

One problem with the use of batteries in stationary applications, suchas in wind farms or in vehicles, such as hybrid or electric vehicles, isto determine the aging status of the individual memory cells (batterycells). The aging status is a characteristic status parameter of thememory cell and is estimated with adequate precision in a suitable wayby determining the internal resistance of the individual memory units,in particular memory cells, by imposing currents of different frequency.This method is performed in validation and test environments usingcomplicated laboratory equipment. For the purpose, the memory unit whoseaging status is to be determined is stimulated with high-power currentsources, and the internal resistance is determined by means of thevoltage change ascertained via the individual memory units.

SUMMARY OF THE INVENTION

The method of the invention is effected by means of a circuitarrangement, in which at least one inductive component and at least onecapacitive component are disposed that with the memory unit form anoscillator circuit; the method has the following steps: exciting theoscillator circuit by means of temporary subjection of the capacitivecomponent to a charge, the exciting being effected by means of anexcitation device supplied electrically by the memory unit; ascertaininga time-dependent voltage change at the capacitive component after thetermination of the excitation; and determining the characteristic statusparameter from the time dependency of the voltage change. In such amethod, the excitation of the memory unit is effected energy-efficientlyand at low expense. Moreover, the method can be employed for variousfrequencies. Since the excitation device is supplied electrically, thatis, supplied with electrical energy, by the electric memory unit itself,an additional energy supply is dispensed with. Since the oscillatorcircuit is excited to oscillation by means of a temporary subjection ofa capacitive component to a charge, and not by a periodic excitation,this excitation can be employed for oscillator circuits of differentnatural frequencies.

The electric memory unit is a unit of a electric memory that as itssmallest unit includes a single electrical memory cell of an electricmemory and as its largest possible unit is the electric memory itself.The electric memory is in particular a rechargeable battery, which ismade up of individual battery cells. The capacitive component is inparticular a capacitor or a capacitor circuit arrangement, and theinductive component is in particular a coil or a coil circuitarrangement. The inductive component has a known inductance L and thecapacitive component has a known capacitance C.

In particular, it is provided that the characteristic status parameteris a state of charge (SOC) and/or an aging status and/or a state ofhealth (SOH) of the memory unit. Preferably, the characteristic statusparameter is the aging status of the memory unit, since this agingstatus exhibits the clearest dependency on the internal resistance ofthe electric memory unit.

In a preferred embodiment of the invention, it is provided that at leastone further capacitive component of the circuit arrangement is connectedin, and for determining the parameter from the changed time-dependentvoltage change, the oscillator circuit is re-excited. By connecting inthe further capacitive component, a changed natural frequency of theoscillator circuit results, and thus a changed “time-dependent “carrierfrequency” of the voltage change.

Preferably, the oscillator circuit, after the time-dependent voltagechange is ascertained, is damped by connecting in at least oneelectrical resistor having a resistance value higher than the internalresistance of the memory unit. By means of this additional damping, thecurrent in the oscillator circuit rapidly diminishes.

It is also advantageously provided that the excitation device hasanother inductive component, which by means of a short-circuit currentbuilds up a magnetic field, and this field, after the shutoff of theshort-circuit current, generates a current flow which temporarilysubjects the capacitive component to charging. The magnetic field thatdiminishes after the shutoff of the short-circuit current induces avoltage which generates the current flow. That flow ensures a chargetransfer to the capacitive component. To prevent an ensuing outflow ofthe charge, a diode is disposed between the other inductive componentand the capacitive component.

The invention further relates to an electric circuit arrangement fordetermining a characteristic status parameter of an electric memory unitthat is dependent on an internal resistance of that memory unit, anaforementioned method. It is provided that the circuit arrangement has acurrent path, which has an inductive component and a capacitivecomponent connected in series and which is electrically connected bymeans of two connection lines to the memory unit for forming anoscillator circuit, and also has an excitation device, suppliedelectrically by the memory unit, which excitation device, for excitingthe oscillator circuit, is interconnected with the capacitive componentby means of a temporary subjection of that capacitive component to acharge. The electric memory unit is a unit of an electric memory, inparticular of a rechargeable battery. The smallest memory unit is asingle memory cell, and the largest memory unit is the electric memoryitself. The inductive component has a known inductance, and thecapacitive component has a known capacitance. The excitation device ispreferably supplied by a partial voltage of the electric memory. Fortapping this partial voltage, the memory unit has at least oneintermediate tap, and the excitation device is supplied electrically viathis intermediate tap and at least one further tap of the memory unit.

In a preferred embodiment of the invention, it is provided that theexcitation device has a short-circuit current path with a switch, theshort-circuit current path being connected parallel to the capacitivecomponent via excitation lines, and the excitation device is connectedto the memory unit via supply lines, and one of the excitation lines hasa diode, and a supply line connected to this excitation line has afurther inductive component. By closure of the switch disposed in theshort-circuit current path, a short-circuit current results which buildsup a magnetic field in the further inductive component. If the switch inthe short-circuit current path is then opened, the short-circuit currentis shut off, and the diminishing induces a voltage peak that is markedlyhigher than the voltage of the memory unit. This voltage peak generatesa current through the excitation line having the diode, which currenttemporarily subjects the capacitive component of the circuit arrangementto a charge. An ensuing reverse flow of the charges in the direction ofthe further inductive component is prevented by means of the diode thatblocks in that direction.

In a further advantageous feature of the invention, it is provided thatthe circuit arrangement has at least one further current path, which isconnected parallel to the capacitive component and has a furthercapacitive component and a further switch connected in series. By meansof this further current path, a further capacitive component that can beconnected in is implemented. The resultant parallel circuit of thecapacitive component and the connected-in capacitive component has atotal capacitance which corresponds to the sum of the capacitances ofthe capacitive component and the further capacitive component. Theresult of this changed total capacitance is an oscillator circuit with adifferent natural frequency.

It is also provided advantageously that the circuit arrangement has atleast one damping current path, which is connected parallel to theinductive component and has a resistor element, having a resistancevalue higher than the internal resistance, and a switch connected inseries. The current through the oscillator circuit can be quicklyreduced to zero by closure of the switch disposed in the damping currentpath.

Finally, it is advantageously provided that the circuit arrangement hasa measuring instrument, which for ascertaining a time-dependent voltagechange at the capacitive component is interconnected with thatcapacitive component. This measuring instrument is preferably connectedto an evaluation device for determining the characteristic statusparameter.

The invention further relates to an electric memory, in particular anelectric memory of an electric drive and/or hybrid drive of a motorvehicle, having at least one electric memory unit and having at leastone aforementioned circuit arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail below in conjunctionwith the associated drawings. In the drawings:

FIG. 1 shows an electric memory unit and an electric circuit arrangementhaving a current path, which has one inductive component and onecapacitive component and is connected to the memory unit and with itforms an oscillator circuit; and

FIG. 2 is a graph in which the time-dependent voltage change at thecapacitive component of FIG. 1 is plotted over time after a respectiveexcitation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an electric memory 2, embodied as a rechargeable battery 1,for electrical supply to an electrical machine, not shown, of anelectric drive of a motor vehicle. The electric memory 2 is formed by anelectric memory unit 3 with electric memory cells 4, 5. The memory cells4, 5 of the rechargeable battery 1 are two battery cells.

FIG. 1 also shows an electric circuit arrangement 6, which is disposedin the motor vehicle between the electric memory unit 3 and an on-boardoperating system, not shown, of the electric drive. The electric circuitarrangement 6 has a current path 7, in which an inductive component 8,embodied as a coil, and a capacitive component 9, embodied as acapacitor, are disposed in series. The current path 7 is connected to apositive contact element 11 of the electric memory unit 3 by means of afirst connection line 10 and to a negative contact element 13 of theelectric memory unit 3 via a second connection line 12. The connectionlines 10, 12 also connect the memory unit 3 to an on-board operatingsystem of the motor vehicle, not shown, which is connectable viaterminals A1, A2.

The electric circuit arrangement 6 furthermore has an excitation device14 for exciting an electric oscillator circuit, formed by the inductivecomponent 8, the capacitive component 9, and an internal resistance ofthe electric memory unit 3, to vanishing. The excitation device 14 has ashort-circuit current path 15, which is connected parallel to thecapacitive component 9 of the second electric memory cell 5. Theshort-circuit current path 15 has a switch 16 and is connected on oneside to negative contact elements 13 of the electric memory unit 3 andto the capacitive component 9, via the second connection line 12embodied as a ground line. On the other, the short-circuit current path15 is connected both to an intermediate tap 19 via a supply line 17, inwhich a further inductive component 18 is disposed, and to the currentpath 7 at a node point 22, via an excitation line 20, in which a diode21 has that blocks a current in the direction of the short-circuitcurrent path 15 and of the further inductive component 18. Parallel tothe capacitive component 9, there are two further current paths 23, 24,which each have one further capacitive component 25, 26 and a respectiveseries circuit with a further switch 27, 28 connected to the associatedcapacitive component 25, 26.

The circuit arrangement 6 furthermore has a damping current path 29,which is connected parallel to the inductive component 8 and has aresistor element 30, with a resistance value that is higher than theinternal resistance R of the electric memory unit 3, and a switch 31 forconnecting in the resistor element 30.

The result is the following function: The excitation of the oscillatorcircuit is effected via the further inductive component 18, the switch16 in the short-circuit current path 15, and the diode 21. The furtherinductive component 18 is connected to a potential lower than the totalvoltage of the electric memory unit 3, which in FIG. 1 is for examplehalf the total voltage of the electric memory unit 3.

At the beginning of the method for determining the characteristic statusparameter, in this case the aging status, that is dependent on theinternal resistance of the memory unit 3, the current I through theinductive component 8 is zero (I=0 A), and the voltage via thecapacitive component 9 is equal to the total voltage of the electricmemory unit 3. The switch 16 in the short-circuit current path istemporarily closed. In this operating mode, the current builds up amagnetic field by means of the further inductive component 18. If theswitch 16 in the short-circuit current path 15 is re-opened, a currentresulting from the inductance L2 of the further inductive component 18flows through the diode 21 to the capacitive component 9 and charges itto a voltage higher than the total voltage of the electric memory unit3. Energy is thus supplied to the oscillator circuit, formed of theinductive component 8, the capacitive component 9, and the internalresistance of the electric memory unit 3. The quantity of energysupplied is determined by a time interval during which the switch 16 inthe short-circuit current path 15 is closed.

The foregoing relates to the preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

Thus a current also now begins to flow through the inductive component 8of the oscillator circuit, whose natural frequency is determined by theinductance L of the inductive component 8 and the capacitance C of thecapacitive component 9. At the capacitive component 9, by means of ameasuring instrument, not shown, a time-dependent voltage change isascertained by measurement. From this, an evaluation device, also notshown, determines the characteristic status parameter of the agingstatus of the electric memory unit 3. The status parameter is aparameter that determines the internal resistance. The status parameterand the internal resistance of the memory unit are therefore parametersdependent on one another.

FIG. 2 shows the voltage course 32 of the voltage at the capacitivecomponent 9 as a function of the time t with the switch 31 of thedamping current path 29 closed, in which course the oscillator circuitis excited every 15 seconds by closure and ensuing opening of the switch16 in the short-circuit current path 15. The voltage course 32 aftereach excitation is determined by a periodic oscillation having thenatural frequency of the oscillator circuit as the carrier frequency andby an exponentially dropping “envelope” 33. The natural frequency of theoscillator circuit is determined by the inductance L of the inductivecomponent and the capacitance C of the capacitive component, while thedamping that determines the envelope is determined by the ohmicresistance and the capacitance C of the oscillator circuit. If theresistor element 30 of the damping path 29 is not connected in, thenthis ohmic resistance value is determined by the internal resistance Rof the memory unit 3.

The invention claimed is:
 1. A method for determining a characteristicstatus parameter of a storage unit by means of an electric circuitarrangement in which at least one inductive component and at least onecapacitive component, which with the storage unit form an oscillatorcircuit, are disposed having the following steps: supplying a voltageproduced by the storage unit to an excitation device, the excitationdevice being connected between the storage unit and the oscillatorcircuit; activating the excitation circuit to excite the oscillatorcircuit temporarily; generating a current flow from the excitationdevice to the oscillator circuit using the voltage in response toactivating the excitation circuit, the current flow temporarilysubjecting the capacitive component to a charge; ascertaining atime-dependent voltage change at the capacitive component aftertermination of the excitation; and determining the characteristic statusparameter from a time dependency of the voltage change.
 2. The method asdefined by claim 1, wherein the characteristic status parameter is oneof a state of charge, an aging status, or a state of health of thestorage unit.
 3. The method as defined by claim 1, wherein a firstinductive component and a first capacitive component of the electriccircuit arrangement are connected in series between a positive and anegative contact of the storage unit to form a first current path,wherein at least one further capacitive component of the circuitarrangement is connected in parallel to the first capacitive component.4. The method as defined by claim 3, wherein the excitation circuit isconnected to a node between the first capacitive component and the firstinductive component, and wherein the at least one further capacitivecomponent of the circuit arrangement is connected to the node inparallel to the first capacitive component.
 5. The method as defined byclaim 4, wherein at least one electrical resistor is connected to thenode in parallel to the first inductive component, the at least oneelectrical resistor having a resistance value higher than an internalresistance of the storage unit for damping the oscillator circuit. 6.The method as defined by claim 1, wherein the excitation device has afurther inductive component for generating the current flow, the furtherinductive component being provided in an excitation line that connects avoltage tap of the storage unit to the node, wherein the excitationdevice includes a short-circuit path that connects the excitation lineto ground and includes a switch for opening and closing theshort-circuit path, wherein the switch is closed to activate theexcitation device to excite the oscillator circuit, wherein ashort-circuit current builds up a magnetic field in the furtherinductive component while the switch is closed, and wherein, when theswitch is opened, the short-circuit current is shutoff and the magneticfield generates the current flow which temporarily subjects thecapacitive component to a charge.
 7. The method as defined by claim 5,wherein the excitation device has a further inductive component forgenerating the current flow, the further inductive component beingprovided in an excitation line that connects a voltage tap of thestorage unit to the node, wherein the excitation device includes ashort-circuit path that connects the excitation line to ground andincludes a switch for opening and closing the short-circuit path,wherein the switch is closed to activate the excitation device to excitethe oscillator circuit, wherein a short-circuit current builds up amagnetic field in the further inductive component while the switch isclosed, and wherein, when the switch is opened, the short-circuitcurrent is shutoff and the magnetic field generates the current flowwhich temporarily subjects the capacitive component to a charge.